Preheat oven to 350 degrees F. Grease an 8x8'' baking dish.
In a large bowl combine the flour, sugar, baking powder, salt, milk, egg and vanilla. Stir in melted butter. Pour mixture into prepared pan and smooth into an even layer.
In a medium bowl, combine the coconut sugar, brown sugar, ground cinnamon, softened butter, and flour. Mix until smooth and creamy.
Pour the cake batter into the prepared baking pan. Spread it out evenly.
Drop spoonfuls of the cinnamon sugar filling over the batter. Use a knife to swirl it into the batter slightly.
Bake in the preheated oven for 30-37 minutes, or until a toothpick inserted into the center comes out clean. Let the cake cool in the pan on a wire rack.
Once the cake has cooled, spread the frosting evenly over the top. Allow it to set slightly before slicing and serving.
